In recent years, introduction of a link aggregation (LA) is under consideration as a technology for improving communication speed in a wireless communication. In the LA, packets to be transmitted over a transport layer connection (e.g., TCP (Transmission Control Protocol) connection) established between a transmission side apparatus and a reception side apparatus are classified and distributed to a plurality of links. That is, in the LA, communication with a total combined bandwidth of all links may be implemented. Further, as for a plurality of links (that is, a plurality of communication schemes) used in the LA, communication schemes in compliance with, for example, LTE (Long Term Evolution) communication standard and WiFi (registered trademark, Wireless Fidelity) communication standard may be considered. FIG. 1 is a diagram illustrating an example of a link aggregation.
When there exist differences in a propagation delay among a plurality of links used in the LA, order of packets arriving at the reception side apparatus may be different from the transmission order (hereinafter, may be referred to as, “out-of-ordering”). FIG. 2 is a diagram illustrating an example of an out-of-ordering of packets.
In a communication over the transport layer such as, for example, TCP, when an omission of a sequence number of the packet arrival order caused by the out-of-ordering is detected, the reception side apparatus transmits “Dup ACK (Duplicate Acknowledgement)” to the transmission side apparatus. That is, the Dup ACK is an ACK packet indicating that the omission of a sequence number of the packet arrival order has occurred. In the meantime, when more than a predetermined number of Dup ACKs are received, the transmission side apparatus determines that a packet loss has occurred at a location midway through a route from the transmission side apparatus to the reception side apparatus. The transmission side apparatus then performs a packet retransmission and, at the same time, decreases a transmission rate of packets. A “congestion window” is used for the control of the transmission rate.
However, when the frequency of receiving more than a predetermined number of the Dup ACKs increases, there is a possibility that the transmission rate is decreased abruptly.
In order to prevent an abrupt decrease of the transmission rate due to an abrupt reduction of the congestion window caused by the out-of-ordering, an “order alignment process” may be performed in a lower layer than the conventional transport layer (see, for example, FIG. 3). The order alignment process may be performed in, for example, an LA layer. For example, in a case where an out-of-ordering occurs in the LA layer, delivery of the received packet to the transport layer is suspended even when the packets transmitted later than the delayed packets have been already received. In the LA layer, the packets are delivered to the transport layer in accordance with the transmission order after the delayed packets have been received. That is, the order alignment process refers to a process in which the order of the received packets is aligned in accordance with the transmission order in the lower layer than the transport layer and the packets are then delivered to the transport layer in accordance with the transmission order. FIG. 3 is a diagram illustrating an example of an order alignment process.
A related technique is disclosed in, for example, Japanese Laid-Open Patent Publication No. 2009-239444.
In the meantime, the transport layer also has a functionality of aligning the order of packets.
That is, when the order alignment process is performed in the lower layer than the transport layer as described above, the order alignment process is performed in the lower layer separately from the order alignment process performed in the transport layer. Therefore, the consumption of the resources of the reception side apparatus such as, for example, a processor resource and a memory resource which temporarily maintains received packets, increases so that there is a possibility that a processing load of the reception side apparatus is increased.